In every example I saw that tries to use a dynamic size for an array in a struct uses global constants at some point. What I am trying to do is pass an integer variable that is decided by the user to a structure that I create storing an array of that size, thus dynamic. Obviously the code below doesn't work, but it gives you an idea of what I plan on accomplishing
struct Node {
char input;
int playingBoard[size];
Node* pNext;
};
int main(){
cout<<"enter board size"<<endl;
cin>>size;
int playingBoard[size];
}
struct Node
{
int countr;
int playingBoard[];
};
int countr;
...
struct Node *p = malloc(offsetof(Node, playingBoard) +
countr* sizeof *p->playingBoard);
p->countr= countr;
...
or an independent dynamically-allocated array
struct Node
{
int countr;
int *playingBoard;
};
Node holder;
...
holder.playingBoard =
malloc(holder.countr * sizeof *holder.playingBoard);
Related
I want to define a constant array of constants at every MPI node using C++03. M_chunk_sizes defines the size of matrix that will be passed to other nodes and won't be changed during the runtime.
int* define_chunk_sizes( int S, int world) {
int out[world];
double quotient = static_cast<double> (S) / world;
int maj = ceil(quotient);
for (int i =0; i < world - 1; i++)
out[i] = maj;
out[world-1] = maj + (S - maj*world);
return out;
}
int main() {
const int M = 999; // rows
int world_size = 4;
const int* const M_chunk_sizes = define_chunk_sizes(M, world_size);
}
But i get a warning: address of stack memory associated with local variable 'out' returned [-Wreturn-stack-address]
return out;.
What is the right way of doing this?
funciton local variables(stack varibales) will go out of scope and life once function returns.
you have use dynamic memory management operators, so allocate memory to out using
new
and relase memory using
delete
once you done with it.
I am trying to solve an issue using Boost multi_index.
If I have 2 structures as follows:
struct MyStruct1
{
int x;
int y;
};
struct MyStruct2
{
int a;
MyStruct1 b;
};
How would I define an index using MyStruct2::b.x?
Is this possible?
was trying something like:
struct xIndex{};
typedef multi_index_container<
MyStruct2,
indexed_by<
ordered_unique<
tag<xIndex>,
member<MyStruct2, int, &MyStruct2::a::x>
>
>
> MyContainer;
But that doesn't work.
Thanks for any info/advice.
There are several ways to accomplish this but all of them require that you write some boilerplate code. The easiest one is providing a user-defined key extractor:
struct MyStruct2XExtractor
{
typedef int result_type;
int operator()(const MyStruct2& m)const
{
return m.b.x;
}
};
...
typedef multi_index_container<
MyStruct2,
indexed_by<
ordered_unique<
tag<xIndex>,
MyStruct2XExtractor
>
>
> MyContainer;
using the uvision IDE for STM32 development, I want to have some timer variables not initialized at startup. I have tried:
volatile unsigned int system_time __attribute__((section(".noinit")));
and
__attribute__((zero_init)) volatile int system_timer;
but nothing seems to work. Following the hints from elswhere, I have additionally checked NoInit at options/target/IRAM1.
Still, the variables are set to zero after reset.
Can anybody help?
You need to follow these steps.
declare your variable as follows:
volatile unsigned int system_time __attribute__((section(".noinit"),zero_init));
Then you have to use a scatter file to declare the execution section with the NOINIT attribute and use it with the linker.
example scatter file:
LR_IROM1 0x08000000 0x00080000 { ; load region size_region
ER_IROM1 0x08000000 0x00080000 { ; load address = execution address
*.o (RESET, +First)
*(InRoot$$Sections)
.ANY (+RO)
}
RW_IRAM1 0x20000000 UNINIT 0x00000100 { ;no init section
*(.noinit)
}
RW_IRAM2 0x20000100 0x0000FFF0 { ;all other rw data
.ANY(+RW +ZI)
}
}
You have to check the address of that variable from .MAP file and use the The at keyword
allows you to specify the address for uninitialized variables in your C source files. The
following example demonstrates how to locate several different variable types using the at keyword.for example......
struct link {
struct link idata *next;
char code *test;
};
struct link idata list _at_ 0x40; /* list at idata 0x40 */
char xdata text[256] _at_ 0xE000; /* array at xdata 0xE000 */
int xdata i1 _at_ 0x8000; /* int at xdata 0x8000 */
char far ftext[256] _at_ 0x02E000; /* array at xdata 0x03E000 */
void main ( void ) {
link.next = (void *) 0;
i1 = 0x1234;
text [0] = 'a';
ftext[0] = 'f';
}
I hope it helps for solving your problem.
I'm new to Objective-C so I'm using a book to get to grips with it. I'm at a bit where it's explaining structs and I can't for the life of me get them to work.
I have the following code:
int main (int argc, char *argv[])
{
struct node
{
int nodeID;
int x;
int y;
BOOL isActive;
};
typedef struct node myNode;
myNode.nodeID = 1;
}
and I'm getting the error written in the title. Every time I search for this error online I found different variations such as 'before '>' token' or 'before '}' token' but i can't find anything with the '.' token and it's really frustrating and I assume it's somethings ridiculously trivial and basic. Any help would be appreciated.
I believe you're trying to modify the actual type itself. nodeA is now the type of that struct, much like int. You need to do something like nodeA myNode, then you would be able to perform myNode.nodeID = 1 without error.
I've got it sorted now, I used the following and it seems to be fixed now:
int main (int argc, char *argv[])
{
struct node
{
int nodeID;
int x;
int y;
BOOL isActive;
};
struct node myNode;
myNode.nodeID = 1;
myNode.x = 100;
myNode.y = 200;
myNode.isActive = TRUE;
}
Thanks for all your help Darth! :)
I think the problem with the original code was, it was trying to make myNode a type name using typedef. Thus, myNode is NOT a variable that assignment can happen to. Rather, it was another alias for struct node.
I'm experimenting with Obj-C blocks and trying to have a struct with two blocks in it where one block is to change what the other block does.
this is a really roundabout way to do something simple... and there may be better ways to do it, but the point of the exercise is for me to understand blocks. here's the code , it doesn't work, so what am I missing/not understanding and/or doing wrong?
//enumerate my math operation options so i can have something more understandable
//than 0, 1, 2, etc... also makes it easier to add operations, as opTypeTotal
//will be 1 plus the index of the operation before it.
typedef enum
{
opTypeAdd = 0,
opTypeSubtract = 1,
opTypeTotal
} opType;
//not sure if (struct someMathStruct)* is correct, probably is wrong
//the intent is to pass a pointer to someMathStruct, but the compiler
//won't know about its existance until a few lines later...
typedef (void)(^changeBlock)(opType,(struct someMathStruct)*);
typedef (void)(^mathBlock)(int,int,int*);
//hold two blocks, to be defined later at runtime
typedef struct someMathStruct{
mathBlock doMath;
changeBlock changeOperation;
} SomeMath;
//i want to declare an array of blocks of type mathBlock
//the intent is to have the array index to correspond with the opTypes enumerated above
//almost certain i'm doing this wrong
mathBlock *m[opTypeTotal] = malloc(sizeof(mathBlock *)*opTypeTotal);
//just two simple math operations as blocks
m[opTypeAdd] = ^(void)(int a,int b,int *result){*result = a+b;};
m[opTypeSubtract] = ^(void)(int a,int b,int *result){*result = a-b;};
//this block is what's supposed to change the other block in the struct
//it takes an opType, and a pointer to the SomeMath struct
//is this the right way to access the member variables of the struct?
changeBlock changeMe = ^(void)(opType a, SomeMath *b) {
//should make adding operations as easy as just adding cases
switch (a)
{
case opTypeAdd: *b.doMath=m[a]; break;
case opTypeSubtract:
default: *b.doMath=m[a]; //catch-all goes to subtracting
}
}
...
SomeMath mathFun;
int theTotal = 0; //a test int to work with
//do i need to copy the changeMe block?
//or can i just do what i'm doing here as the block itself isn't unique
mathFun.changeOperation = changeMe;
mathFun->changeOperation(opTypeAdd, &mathFun);
mathFun->doMath(theTotal,11,&theTotal); //result should be 11
mathFun->changeOperation(opTypeSubtract, &mathFun);
mathFun->doMath(theTotal,3,&theTotal); //result should be 8
NSLog(#"the result: %d",theTotal); //should output "the result: 8"
The code seems to work as you expect (the result is 8) once you fix the compilation errors:
Compile with: gcc -o test test.m -framework Foundation
#import <Foundation/Foundation.h>
//enumerate my math operation options so i can have something more understandable
//than 0, 1, 2, etc... also makes it easier to add operations, as opTypeTotal
//will be 1 plus the index of the operation before it.
typedef enum
{
opTypeAdd = 0,
opTypeSubtract = 1,
opTypeTotal
} opType;
struct someMathStruct; // Forward declare this as a type so we can use it in the
// changeBlock typedef
typedef void (^changeBlock) (opType,struct someMathStruct*);
typedef void (^mathBlock) (int,int,int*);
//hold two blocks, to be defined later at runtime
typedef struct someMathStruct{
mathBlock doMath;
changeBlock changeOperation;
} SomeMath;
int main()
{
//i want to declare an array of blocks of type mathBlock
//the intent is to have the array index to correspond with the opTypes
// enumerated above
mathBlock *m = calloc(opTypeTotal, sizeof(mathBlock *));
//just two simple math operations as blocks
m[opTypeAdd] = ^(int a,int b,int *result){*result = a+b;};
m[opTypeSubtract] = ^(int a,int b,int *result){*result = a-b;};
changeBlock changeMe = ^(opType a, SomeMath *b) {
//should make adding operations as easy as just adding cases
switch (a)
{
case opTypeAdd: b->doMath = m[a]; break;
case opTypeSubtract:
default: b->doMath = m[a]; //catch-all goes to subtracting
}
};
SomeMath mathFun;
int theTotal = 0; //a test int to work with
mathFun.changeOperation = changeMe;
mathFun.changeOperation(opTypeAdd, &mathFun);
mathFun.doMath(theTotal,11,&theTotal); //result should be 11
mathFun.changeOperation(opTypeSubtract, &mathFun);
mathFun.doMath(theTotal,3,&theTotal); //result should be 8
NSLog(#"the result: %d",theTotal); //should output "the result: 8"
}